CoreData, many-to-many relationships and NSPredicate

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渐次进展 2021-01-01 06:28

I have a CoreData datamodel that includes a many-to-many relationship. As it turns out NSPredicate does not support many-to-many relationships. From CoreData.pdf: \"You can

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  •  北荒
    北荒 (楼主)
    2021-01-01 07:01

    This question actually led me down the wrong path with a problem I was having. It turns out you can query a many-to-many relationship with a predicate. You just can't query further down like A <<-->> B <<-->> C

    The predicate I used (in a model with Story <<-->> Team) was this...

    [NSPredicate predicateWithFormat:@"SUBQUERY( teams, $t, $t IN %@ ).@count > 0", teams)];
    

    This predicate is used in a fetch request against the Story entity. The second "teams" is a set or array of teams I am searching for stories about. The SUBQUERY format is a bit confusing to me, so I'll note it can be read as, "For each team t in the current story's teams collection, see if it is in this other collection (teams)."

    Hope this helps.

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